US3769812A

US3769812A - Compressor lubrication apparatus for closed reversible cycle ice-making systems

Info

Publication number: US3769812A
Application number: US00257299A
Authority: US
Inventors: R Gordon
Original assignee: Individual
Current assignee: Individual
Priority date: 1972-05-26
Filing date: 1972-05-26
Publication date: 1973-11-06
Anticipated expiration: 1990-11-06

Abstract

Apparatus for concurrently circulating a refrigerant and a refrigerant oil through a closed reversible cycle ice-making system having interconnected compressor, condenser and evaporator components and in a manner which provides efficient heat exchange, capacity and compressor lubrication. The invention is characterized by a combination of three interdependent features, namely, (1) During the ice-forming phase, an emulsion of a refrigerant and a refrigerant oil is caused to flow through the evaporator chamber at sufficient velocity and turbulence to prevent substantial adherence of the oil to the chamber side walls and to produce substantially uniform freezing temperatures on the wall surfaces; (2) During the alternate defrosting phase and when the emulsion has separated into hot gaseous refrigerant and refrigerant oil, the gaseous refrigerant is caused to flow through the chamber at sufficient velocity to suspend the oil and sweep it from the chamber walls, and (3) During both of said phases, a positive pressure drop across the evaporator chamber is maintained within the range of 0 lbs./sq. in. to 2 lbs./sq. in. to thereby create a balanced efficiency between oil circulation and heat exchanger on one hand, and the capacity of the system on the other.

Description

United States Patent 1 Gordon 1 Nov. 6, 1973 COMPRESSOR LUBRICATION APPARATUS FOR CLOSED REVERSIBLE CYCLE ICE-MAKING SYSTEMS [76] Inventor: Robert W. Gordon, PO. Box 606,

Longwood, Fla. 32750 [22] Filed: May 26, 1972 [21] Appl. No.: 257,299

Primary Examiner-William E. Wayner Attorney-Robert Brown, Jr.

[57] ABSTRACT Apparatus for concurrently circulating a refrigerant and a refrigerant oil through a closed reversible cycle ice-making system having interconnected compressor, condenser and evaporator components and in a manner which provides efficient heat exchange, capacity and compressor lubrication. The: invention is characterized by a combination of three interdependent features, namely, (1) During the ice-forming phase, an emulsion of a refrigerant and a refrigerant oil is caused to flow through the evaporator chamber at sufficient velocity and turbulence to prevent substantial adherence of the oil to the chamber side walls and to produce substantially uniform freezing temperatures on the wall surfaces; (2) During the alternate defrosting phase and when the emulsion has separated into hot gaseous refrigerant and refrigerant oil, the gaseous refrigerant is caused to flow through the chamber at sufficient velocity to suspend the oil and sweep it from the chamber walls, and (3) During both of said phases, a positive pressure drop across the evaporator chamber is maintained within the range of 0 lbs/sq. in. to 2 lbs/sq. in. to thereby create a balanced efficiency between oil circulation and heat exchanger on one hand, and the capacity of the system on the other.

1 Claim, 3 Drawing Figures AAA.

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COMPRESSOR LUBRICATION APPARATUS FOR CLOSED REVERSIBLE CYCLE ICE-MAKING SYSTEMS This invention relates to lubrication and more particularly to a closed reversible cycle ice-making system having improved heat exchange, oil return to the compressor, and capacity operation.

The present invention is adapted to be associated with conventional automatic ice-making systems such as disclosed in US. Pat. No. 3,146,610 and which are provided with a compressor, a condenser and an evaporator. In such systems, the evaporator usually comprises upright concentrically spaced tubular members between which a fluid media consisting of an emulsion of a refrigerant and a refrigerant oil flows in condensed liquefied form during the ice-forming phase, and between which the refrigerant in a hot gaseous form and the separated refrigerant oil flow during the iceharvesting or defrosting phase. Heretofore, the refrigerant and oil have been conducted through the evaporator chamber without due regard to the basic principles of hydraulic flow and, consequently, highly localized eddy and counteracting currents have produced wide variations in heat exchange, excessive pressure drops and oil accumulation in the evaporator chamber resulting in defective compressor lubrication, and also a reduction in the overall capacity of the system (See US. Pat. No. 3,327,494). In the latter patent, the lack of uniformity of heat exchange inthe refrigerant chamher was of primary concern, and especially with respect to the excess heat exchange and ice formation at the bottom of the evaporator coupled with a deficiency at the top. The solution proposed in this patent, however, was inadequate because the oppositely acting refrigerantjets promoted more turbulence at the bottom of the chamber without increasing the turbulence in the upper portions thereof, resulting in an excess ice accumulation at the bottom as well as a less efficient oil return to the compressor.

It is therefore an object of this invention to create a concurrent flow of refrigerant and refrigerant oil through the evaporator of an ice-making system of the class described, which flow will produce substantially uniform freezing temperature throughout the evaporator chamber during the ice-forming phase, and will further produce in the chamber a suspension of the oil in the gaseous refrigerant during the defrosting phase to thereby prevent the oil from becoming logged in the evaporator.

It is another object of this invention to provide a system of the class described having a balanced efficiency as between oil circulation and ice producing heat exchange on one hand, and the overall capacity of the system on the other. In this connection, it should be noted that the conditions favoring uniform freezing temperature and the efficient oil suspension in the evaporator chamber are opposed to those favoring a high capacity of the system. High refrigerant velocity and uniform turbulence tend to effect a more efficient heat transfer, and also tends to keep the oil insuspension during the defrosting phase. Nevertheless, the high velocity tends to produce an undesirable pressure drop which, in turn, promotes inefficient operation of the system. Therefore, a compromise condition is adopted which permits the opposing conditions to serve their respective goals. Extensive research has proven that a pressure drop in the evaporator chamber ranging between 0 lbs/sq. in. and 2 lbs/sq. in. are critical limits satisfying the opposing conditions. By confining the pressure drop to this range, neither of the heat exchange, oil circulation, nor the system capacity factors will be increased or diminished to a serious detriment of the others.

Some of the objects of invention having been stated, other objects will appear as the description proceeds when taken in connection with the accompanying drawings, in which,

FIG. 1 is an elevational view of an evaporator according to the invention with certain portions thereof broken away and other portions in section, and further showing schematically an associated refrigerating system for making ice;

FIG. 2 is a sectional plan view of the top portion of the evaporator and taken along line 2-2 in FIG. 1; and

FIG. 3 is a sectional plan view taken along line 3-3 in FIG. 1.

Referring more particularly to the drawings, the numeral 10 indicates broadly an evaporator comprising an upright outer tubular member 11, a substantially concentric inner tubular member 12, and an annular refrigerant chamber 14 separating the two members said chamber being substantially free of any fluid guide means. Chamber 14 is sealed at its top by means of a plate 15 and at its bottom by an outwardly flared end or skirt of inner tubular member 12.

Surfaces lla and 12b of

members

11 and 12 respectively are sprayed with water from

spray heads

16 and 17 concurrently with the flow of a refrigerant through chamber 14 thereby causing ice to form on these surfaces during the freezing phase of an operating cycle. The freezing phase is followed by a defrosting or iceharvesting phase during which hot gaseous refrigerant is caused toflow through chamber 14 to release the ice from surfaces 11a and 12b. In order to properly lubricate the system, and especially the compressor 27 thereof, a suitable refrigerant oil is added to the refrigerant.

The refrigerant and refrigerant oil are introduced into chamber 14 by means of an injector tube 18, which tube extends downwardly through plate 15 into and near the bottom of the chamber. The tube has an arcuate laterally extending lower end portion 18a provided with orifice 18b for directing the refrigerant and oil substantially tangentially of the chamber centerline 14a and against the concave inner wall surface 1 1b of tubular member 11, said refrigerant and oil then deflecting from surface 11b to thereafter flow circumferentially and unidirectionally about the centerline 14a as it swirls in a cyclonic manner upwardly toward outlet 20 at the top of the chamber.

Although the refrigerant and oil swirl at a maximum velocity at the point of discharge 18b andwith some decrease in velocity as it travels upwardly, the velocity is always sufficient to produce substantially uniform freezing temperature on the ice-forming surfaces of the chamber. In fact, it is necessary to have some decrease in velocity in order to prevent an undesirable pressure drop in the evaporator. As a result of the unidirectional swirling action and turbulence, a uniform thickness of ice is produced upon the surfaces lla and 12b. Moreover, this velocity and turbulence is especially desirable during the defrosting cycle to keep the oil suspended in the hot gaseous refrigerant and keep it moving through the evaporator and back to the compressor 27.

It is important to note that the injector tube is employed for circulating fluids into chamber 14 during both the freezing and harvesting phases of operation. The upper end of tube 18 communicates with refrigerant supply circuit through a line 23 and a hot gaseous defrost circuit through line 25a. The refrigerant supply is controlled by an external equalized expansion valve 22 during the ice-forming phase, and the hot gaseous refrierant supply is controlled by gas valve 24, said valves being operated alternately in a conventional manner during the freezing and harvesting phases. By suitably altering the configuration of tube portion 18a and/or the sizes of openings 18b and and by creating a substantially uniformly distributed helical unidirectional flow from the bottom to the top of chamber 14, the positive pressure drop across the evaporator chamber (i.e. between orifice 18b and outlet 20) may be limited to the critical value of not more than 2 lbs./sq. in.

The above-described system may comprise the compressor 27, a condenser 28, a heat exchanger 29, and a surge tank 30. Members 27 through 30 are connected as follows: high pressure discharge line 31 connects compressor 27 to line line 25 connects line 31 to the upper portion of condenser 28; line 32 connects the lower portion of the condenser to the lower portion of heat exchanger 29; line 33 connects the upper portion of the heat exchanger to external equalized expansion valve 22, said connections being located on the pressure side of the compressor. On the suction side of the compressor, line 36 leads through heat exchanger 29 and into the upper portion of surge tank and another line leads from the upper portion of said tank to the evaporator outlet 20. A suitable coolant such as water enters condenser coil 39 as at 40 and leaves the coil as at 41.

During the freezing phase, valve 24 is closed, at which time the compressed hot gaseous refrigerant and refrigerant oil flow from compressor 27, through lines 31 and 25 and condenser 28 to extract heat therefrom and thereby form a liquid emulsion of the refrigerant and the oil. From the condenser 28, the emulsion continues to travel through the heat exchanger 29, line 33, expansion valve 22, line 23, injector tube 18, chamber 14, surge tank 30, suction line 36, and back to the compressor. While the emulsion is in chamber 14, it separates into refrigerant gas and oil components, at which time the oil tends to settle rather than travel with the gaseous component.

During the ice-harvesting phase, the valve 24 is opened to permit the hot gaseous refrigerant and the oil to flow from the compressor 27, through line 31, line 25a, valve 24, injector tube 18, chamber 14, line 35, surge tank 30, line 36, and back to the compressor. Unless sufficient velocity of the hot gaseous refrigerant is maintained to keep the oil in suspension, the abovementioned tendency for theoil to settle will occur and thus restrict oil circulation and lubrication of the component parts of the system. 1 1

The above-described ice-producing and lubricating apparatus may be operated automatically in a wellknown manner by circuitry such as shown in the aforementioned US. Pat. No. 3,146,610.

The following basic facts emphasize the importance of the construction and method steps employed to properly lubricate the ice-making system:

In a mechanical refrigeration system, the return of the oil to the compressor is of critical importance. The oil in the refrigerant is the only means of lubrication of the compressor and the lack of it is the most common cause of compressor failure. Hence, an adequate amount of oil must always circulate with the refrigerant.

Liquid refrigerant is miscible with oil. The refrigerant gas and oil, however, do not mix readily and the oil can be properly circulated through the system only if the design is such that the velocity of the refrigerant in its gaseous state is great enough to sweep the oil along. If the velocities are not sufficiently high, the oil will tend to lie on the bottom of the refrigerant tubing and the evaporator and cling to the evaporator walls, thereby causing oil clogging and decreasing the heat transfer capability of the evaporator due to the insulating effect of the oil. As more oil is trapped in the system, a shortage could develop in the compressor causing bearing failure.

As the evaporating temperatures are lowered, the problem becomes more critical since the viscosity of the oil increases with the decrease in temperature. For this reason, proper velocity control and turbulence are essential for satisfactory oil return. Several factors combine to make oil return most critical at low evaporating temperatures. As the suction pressure decreases and the refrigerant vapor becomes less dense, the more difficult it becomes to sweep the oil along. At the same time, as the suction pressure falls the compressor ratio increases and as a result the compressor capacity decreases. Refrigerant oil at 0F. takes on the consistency of molasses, but as long as it is mixed with sufficient liquid refrigerant, it flows freely. As the percent of the oil in the mixture increases, the viscosity increases requiring greater velocity and turbulence to move it along. At low temperature, all these factors start to converge and tend to create a critical condition in which the density of the gas decreases, the mass velocity flow decreases, and as a result, more oil starts to accumulate in the evaporator.

As the oil and refrigerant mixture becomes more viscuous, at some point the oil starts logging in the evaporator rather than returning to the compressor, resulting in wide variations in the compressor crankcase oil level. This condition will not occur if sufficient velocity and turbulence is created in the evaporator. The present evaporator design, when operated in accordance with the herein disclosed method, creates sufficient uniform velocity and turbulence to overcome this problem even at extremely low temperatures.

Although turbulence is desired and in fact essential to effect a more efficient heat transfer, it has not been satisfactorily attained heretofore in conjunction with adequate compressor lubrication, insofar as I am aware. As the pressure leaving the evaporator at outlet 20 is decreased, the specific volume of gas returning to the compressor increases and the weight of the refrigerant pumped by the compressor decreases. Therefore, the pressure drop in the evaporator causes a decrease in system capacity.

it is important to note that the refrigerant oil tends to become unsuspended and accumulate within the evaporator 10 during the freezing phase as well as during the defrosting phase. During the freezing phase, the liquid enters the evaporator at 18b and immediately expands into a gas state. Therefore, the oil tends to precipitate out of the gas and cling to the walls of chamber 14, especially in the uppermost portions of the chamber. Hence, the necessity of limiting the pressure drop to the critical maximum continues during the freezing phase.

The goals of low pressure and high velocity are directly opposed; consequently, the evaporator design must be a compromise. In the present design, a uniform turbulence is created which keeps the oil swept from the walls of the evaporator during both phases, increases the heat transfer throughout the evaporator, and causes a pressure drop of not more than 2 p.s.i. in the evaporator. This lack of pressure beyond this limit will cause the compressor to draw less power in its operations, resulting in more efficiency for less operating cost.

Briefly stated, the present method and apparatus creates a more uniform velocity and turbulence in the evaporator which, in turn, creates a more uniform heat transfer throughout the length of the evaporator and contributes to more efficient ice production; creates better oil return to the compressor, reducing the possibility of compressor failure, and reduces the evaporator drop to not more than 2 p.s.i., resulting in a more efficient system.

I claim:

1. Compressor lubrication apparatus for a closed re- 6 versible cycle ice-making system comprising: a con denser; a compressor; an evaporator, said evaporator including a pair of spaced upright substantially concentric members forming a sealed annular chamber therebetween, said chamber being substantially free of any fluid guide means between the inner opposed walls thereof, the respective areas of said members remote from the chamber defining ice-forming surfaces; means including said compressor for circulating during the freezing phase a refrigerant-oil media under high pressure an upwardly and unidirectionally in a helical path extending from the bottom to the upper portion of said chamber; and means including said compressor for circulating during the alternate defrosting phase the separated refrigerant and oil of said media under relatively low pressure and upwardly and unidirectionally in said helical path, said last-named means consisting of an inlet nozzle positioned horizontally and tangentially at the bottom portion of the chamber and adapted to direct the media into one end of said helical path, and an outlet at the upper portion of the chamber communicating with the other end of said path, whereby the velocity and turbulence of the media will produce asubstantially uniform heat exchange in the chamber while preventing a pressure drop across the chamber as a result of the accumulation of unsuspended oil therein.

Claims

1. Compressor lubrication apparatus for a closed reversible cycle ice-making system comprising: a condenser; a compressor; an evaporator, said evaporator including a pair of spaced upright substantially concentric members forming a sealed annular chamber therebetween, said chamber being substantially free of any fluid guide means between the inner opposed walls thereof, the respective areas of said members remote from the chamber defining ice-forming surfaces; means including said compressor for circulating during the freezing phase a refrigerant-oil media under high pressure an upwardly and unidirectionally in a helical path extending from the bottom to the upper portion of said chamber; and means including said compressor for circulating during the alternate defrosting phase the separated refrigerant and oil of said media under relatively low pressure and upwardly and unidirectionally in said helical path, said last-named means consisting of an inlet nozzle positioned horizontally and tangentially at the bottom portion of the chamber and adapted to direct the media into one end of said helical path, and an outlet at the upper portion of the chamber communicating with the other end of said path, whereby the velocity and turbulence of the media will produce a substantially uniform heat exchange in the chamber while preventing a pressure drop across the chamber as a result of the accumulation of unsuspended oil therein.